1. Field of the Invention
The invention relates to equipment for a bed, especially a hospital or a care bed, and to a method for measuring whether a bed sheet is wet.
2. The Prior Art
The invention is primarily aimed at equipment for mounting on a bed for a safe indication whether the bed has become wet. The problem may arise if a person suffers from incontinency or profusely sweating. As far as children in the home as well as elderly persons within the nursing or hospital sector are concerned, it is desirable to achieve a safe indication whether the bed is wet. The desire originates in ethical and human respect, hygienic reasons, and for reasons of health. When a situation occurs where the bed has become wet, it is desirable to secure a safe and reliable indication for a fast relief of the problem, by warning the nursing staff that cleaning of the bed is required.
One kind of equipment for indicating whether a bed has become wet is a bed-wetter sheet. An example of a bed-wetter sheet is known from U.S. Pat. No. 2,668,202 (B. D. Kaplan). The bed-wetter sheet simply consists of a bed sheet with built in electrodes from which one can measure the mutual electrical isolation of the electrodes. The electrodes can be arranged parallel at one layer of the sheet, or be arranged at separate layers of the sheet. When the sheet is dry, the resistance will be high, whereas the presence of fluid will change the resistance between the electrodes, and especially when the fluid comprises salt, as it is the case where body fluids are concerned.
A measuring method for indication of a wet bed-wetter sheet is known form U.S. Pat. No. 4,347,503 (Otto A. Uyehara), whereby an electric circuit on a regular basis sends electric pulses to the electrodes of the bed-wetter sheet. When the sheet is wet, the impulses are lead through the sheet and will trigger a relay function in the form of a thyristor whereby an alarm is activated.
The bed-wetter sheet and the appliance for indication of a wet sheet is in a way an excellent solution, because the bed-wetter sheet can be washed and used again, besides it is also inexpensive and practical. The appliance for indicating when a sheet is wet is furthermore excellent, because voltage is not continuously impressed. The alarm function is also power-saving in that the pulses are sent only periodically, and in that way keeps the measuring equipment in a power-saving resting state most of the time.
However, the appliance has certain disadvantages as the system cannot indicate whether the electrodes are connected to the measuring circuit. The connection might be disconnected when the patient twitches the cables unintentionally, or when the nursing staff is carrying out their work with the patient. A faulty mounting of the electrodes when the equipment is mounted in the bed might also happen. Another faulty situation might happen when the electrodes in the sheet due to wear, by lapse of time or frequently washing are broken, and the lengths of the electrodes hereby have been diminished. It will thus not be possible to have an indication of that the bed is wet at a random point of the sheet, but only in the area where the electrodes are intact.
Another disadvantage of the equipment is that the measuring circuit is supplied from a battery which means that it has to be secured that the battery continuously is in a position to supply energy. The solution does not focus on personal safety or personal comfort either. The patient is in close contact with the wet area of the sheet which is why even a faint measuring current would bother the user. Especially when it comes to pulsing voltage, as stated in prior art, where the presence of a coil which is connected and disconnected could induce high levels of voltage on the electrodes of the bed-wetter sheet.
The purpose of the invention is therefore to provide a solution which is fail safe in connection with monitoring of a bed, and to indicate whether the bed is wet, and at the same time provides a solution which is inexpensive and simple. At the same time is requested a solution which takes personal safety and personal comfort into consideration.